Finite Element Modeling and Validation of the Patellofemoral Joint

The patellofemoral joint is part of the knee joint, which is considered the largest joint in the human body. The patellofemoral joint is composed of the patella, a flat, rounded triangular bone, the distal part of the femur, which forms an inverted U-shaped intercondylar groove, and the articular cartilage that covers both the distal femur and posterior patella. Articular cartilage has several functions to enhance functionality in this joint (e.g., reduce friction, shock absorption, load distribution). Patellofemoral disorders are a leading cause of knee pain and cartilage degeneration, with a diagnosis of 1.5%-7.3% of all patients seeking medical care within the United States. Females experience patellofemoral pain more often than males, and the pain increases with age (the 50-59-year-old age group had the most cases). The most relevant patellofemoral joint diseases are associated with overuse, repetitive stress, muscle imbalance, misalignment, or poor patellar tracking because the kneecap may not move appropriately along the femoral groove during flexion and extension. A non surgical approach is usually preferred for these pathologies, but the failure of conservative management will result in exploring surgical approaches. A common surgical treatment when conservative treatments fail is Tibial Tubercle Osteotomy (TTO), which consists of the realignment of the patellar tendon, moving the tibial tubercle, where the patellar tendon is inserted. This thesis is part of a larger project whose final goal is to obtain a validated finite element modeling framework that can predict patellofemoral contact mechanics and changes after TTO surgery, assess patients before surgery, and plan the surgery accordingly with quantified measurements. The aim is to obtain the best surgical outcome possible and plan the surgery accordingly. Based on this final goal, the primary specific goal of this study is to develop a pipeline to create patient-specific models of the patellofemoral joint from clinical images (MRI), starting with cadaver specimens. Once the workflow is established and the baseline patellofemoral joint model is created, the secondary goal is to evaluate its sensitivity to numerical parameters and uncertainties arising during its development. Finally, the last goal to validate the pipeline is to compare the FE model results of these cadaveric models created with experimental results derived from cadaveric experiments. This validation will be useful to quantify the trustability and accuracy of the created pipeline. Contact pressure between patella articular cartilage and femur articular cartilage will be the primary variable in evaluating results. Once validated, the pipeline will be used to create patient models. In particular, 10 knees of subjects with abnormal sagittal tubercle-trochlear groove distances will be analyzed with the aim of identifying some anatomical predictors of surgical success by comparing initial anatomy and the outcome of 5mm and 10mm anteriorization of the tibial tubercle. The project has some limitations related explicitly to non-patient-specific parameters used, such as material properties of bones, cartilage, and soft tissue, geometrical aspects of soft tissue, and ideal waveform as boundary conditions to simulate squatting movement. Overall model behavior, sensitivity studies, and comparison to experiments suggests that it can be a valuable tool in surgical planning and patient assessment.